Gross premiums written shall comprise all amounts due during the financial year in respect of insurance contracts regardless of the fact that such amounts may relate in whole or in part to a later financial year, and shall include inter alia: ii(i) premiums yet to be written, where the premium calculation can be done only at the end of the year: i(ii) - single premiums, including annuity premiums, - in life assurance, single premiums resulting from bonus and rebate provisions in so far as they must be considered as premiums on the basis of contracts and where national legislation requires or permits their being shown under premiums ...